The present invention relates to the field of lined explosive charges for perforating targets. More particularly, the present invention relates to a disk shaped component in a shaped charge liner for producing a material penetrating jet to produce a large target perforation downhole in a wellbore.
The invention is particularly useful in the field of downhole well casing perforations. Well casing is typically installed in boreholes drilled into subsurface geologic formations. The well casing prevents uncontrolled migration of subsurface fluids between different well zones and provides a conduit for production tubing in the wellbore. The well casing also facilitates the running and installation of production tools in the wellbore. Well tubing can be installed within well casing to convey fluids to the well surface.
To produce reservoir fluids such as hydrocarbons from a subsurface geologic formation, the well casing is perforated by multiple high velocity jets from perforating gun shaped charges. A firing head in the perforating gun detonates a primary explosive and ignites a booster charge connected to a primer or detonator cord. The detonator cord transmits a detonation wave to each shaped charge.
In a conventional shaped charge, booster charges within each shaped charge activate explosive material which collapse a shaped liner toward the center of a cavity formed by the shaped charge liner. The collapsing liner generates a centered high velocity jet for penetrating the well casing and the surrounding geologic formations. The jet properties depend on the charge case and liner shape, released energy, and the liner mass and composition. Shaped charge jets perforate the well casing and establish a flow path for the reservoir fluids from the subsurface geologic formation to the interior of the well casing. This flow path can also permit solid particles and chemicals to be pumped from the casing interior into the geologic formation during ravel packing operations.
Various efforts have been made to modify the performance of shaped charges. Barriers and voids have been placed within the explosive material to modify the detonation wave shape collapsing the liner. Examples of detonation wave shaping techniques are described in U.S. Pat. No. 4,594,947 to Aubry et al. (1986), U.S. Pat. No. 4,729,318 to Marsh (1988), and U.S. Pat. No. 5,322,020 to Bernard et al. (1984). In each of these patents, detonation wave shapers are positioned in the explosive material between the detonator cord and the liner. In U.S. Pat. No. 5,753,850 to Chawla et al. (1998), a spoiler was positioned within the liner cavity to modify the perforating jet shape.
Other efforts have been made to modify perforating jet performance by changing the liner shape. In U.S. Pat. No. 3,268,016 to Bell (1964), a disk-like appendage in a liner was provided to peen the rough perforation burr after the leading perforating jet portion penetrated through the target. The disk-like appendage was configured to form a slug portion with a diameter larger than the perforating jet entry hole diameter. In U.S. Pat. No. 5,559,304 to Schweiger et al. (1996), a liner having a flattened outer surface for the purpose of stretching and flattening the perforating jet shape. The flattened central region of the liner apex reduced the thickness of the liner between 10-15 percent. The velocity of the perforating jet was reduced to enhance stable flight and end-ballistic performance. In U.S. Pat. No. 4,702,171 to Tal et al. (1987), the liner apex was hollowed, and in U.S. Pat. No. 3,137,233 to Lipinski (1962), a conical liner represented a squared liner apex in one view for the purpose of facilitating the liner manufacture.
One technique for generating a large diameter perforation uses a mandrel to shape the perforating jet shape. In U.S. Pat. No. 4,841,864 to Grace (1989), a mandrel was placed along the liner longitudinal axis to control the perforating jet shape. In U.S. Pat. No. 5,155,297 to Lindstadt et al. (1992), a solid weight member was centrally positioned in the liner to stabilize the deformation of the perforating jet. The weight member extended into the explosive charge and through the liner material.
Another technique for generating a larger perforating hole incorporates a liner having a hemispherical portion attached to a conical skirt. Because the hemispherical portion has a discontinuity in the liner slope, a negative velocity gradient creates a bulge in the material perforating jet which leads to a larger hole in the target material. Although a larger hole is created, the size of the hole is limited by the configuration of the composite liner surfaces.
In certain well completion activities such as gravel packing operations, large diameter well perforations are desirable to facilitate the rapid placement of solid particles into the well. To accomplish this objective, a perforating gun should remove a large target surface area from the casing before the energy of the perforating jet is expended. Conventional shaped charge techniques are limited in their ability to generate large casing holes without significantly increasing the shaped charge size. Accordingly, a need exists for an apparatus that can efficiently create large diameter perforations or minimum penetration in well casing and other selected targets.